For the first one, work on your proportions. A good guideline is to make your normal adult figures eight heads tall. Yours is about six. Because he's a knight/warrior of some sort, his shoulders should be broader as well. It will make him look more commanding. Right now he looks like a 12 year old, which doesn't fit with the costume he's wearing.

I think the last one is my favorite, even though there's not much there yet. The shading looks good, and the demon is appropriately terrifying.

This may sound weird, but I think your best sketch is the lightly drawn bird in the lower right corner of the second pic. It has looseness and life to it.
The other drawings seem a little overworked. The outlines aren't always clean, and sometimes the shading and the outline seem to be fighting each other. For example, look at the feet of the warrior character. They are defined mostly by outlines, with a little bit of shading. But if you look at the sword, it is defined mostly by shading, with the outline just offering support.
You should pick one way of doing things and stick with it. The demon head in the last pic is more consistent. It is defined mostly by shading, with outlines used as needed.

Mmm, I like that first one. It has a good environment/composition going.
You seem to have darker darks in these latest. Are you doing something different or did you adjust it after scanning?
I like the higher contrast.